"Hellfire" hands down! The song itself is just so powerful and then you get to what it's actually about! I love how dark it is! The whole soundtrack is amazing (same with Pocahontas)
Another one of my favorite villain songs is "Whose been painting my roses red?" from Alice in Wonderland.
Oh and "Be Prepared" gets a vote too just for the lines
We'll have food!
Lots of food!
hehehe! Makes me laugh every time!
Now, if you smell the roses but it doesn't lift your spirits, you're either allergic to rose pollen or you need medical intervention. ~ Seshat